In the future, it is expected that electric vehicles and plug-in type hybrid vehicles are spread, so that it is considered that load applied to equipment such as distribution substations and pole transformers in the power system which supplies electric power to consumers is increased. In the power system, when the load exceeding a permissible value is applied to the equipment, a variety of trouble occurs to be exposed to danger. For example, when the load exceeding the permissible value is applied to the distribution substation, a breaker in the distribution substation is operated, so that an outage occurs in the whole region. Further, when the load exceeding the permissible value is applied to the pole transformer, the pole transformer is sometimes burned and damaged.
As the technique of solving such an overload state, there is a technique disclosed in the non-patented literature 1. In the technique of the non-patented literature 1, first, when the overload state of the pole transformer is detected, a load control volume required to solve the overload is calculated. Next, an amount of load to be reduced when apparatuses of consumers constituting the load are stopped, that is, power sources are cut off is predicted. Until the load control volume required to solve the overload state is reached, the amount of load reduced by stopping the apparatuses of consumers is added up. The apparatuses of consumers requested to be stopped are decided on the basis of the added-up results and a stop request signal is transmitted to the relevant apparatuses of consumers. The apparatuses of consumers which receive the stop request signal cut off their power sources. Consequently, the load on the equipment is reduced to solve the overload state.